Internal combustion engines fluidly couple to exhaust aftertreatment systems that purify exhaust gases generated as a byproduct of combustion. Exhaust aftertreatment systems may include oxidation catalysts, reduction catalysts, selective catalytic reduction catalysts and particulate filters.
Internal combustion engines also employ sensors to monitor an entrained exhaust gas feedstream for purposes of engine control and diagnostics. Known sensors include zirconium-based oxygen sensors, wide-range lambda sensors, and constituent sensors such as NOx sensors. Such sensors may include integrated electrical heaters to heat a sensing element, thus improving measurement repeatability.
Sensors monitoring an exhaust gas feedstream may experience fouling caused by deposition of unburned hydrocarbons and particulate matter. Such fouling may occur under low temperature operating conditions, such as immediately after engine cold starting. Such fouling may also occur during execution of engine operating conditions that include running in a rich air/fuel condition to generate unburned hydrocarbons that flow into an oxidation catalyst for heat generation upstream of a selective catalytic reduction catalyst. Particulate matter may be generated in an internal combustion engine operating in a compression-ignition state.